Nanotube dispersants and dispersant free nanotube films therefrom

ABSTRACT

A degradable polymeric nanotube (NT) dispersant comprises a multiplicity of NT associative groups that are connected to a polymer backbone by a linking group where there are cleavable groups within the polymer backbone and/or the linking groups such that on a directed change of conditions, bond breaking of the cleavable groups results in residues from the degradable polymeric NT dispersant in a manner where the associative groups are uncoupled from other associative groups, rendering the associative groups monomelic in nature. The degradable polymeric nanotube (NT) dispersant can be combined with carbon NTs to form a NT dispersion that can be deposited to form a NT film, or other structure, by air brushing, electrostatic spraying, ultrasonic spraying, ink-jet printing, roll-to-roll coating, or dip coating. The deposition can render a NT film that is of a uniform thickness or is patterned with various thicknesses. Upon deposition of the film, the degradable polymeric nanotube (NT) dispersant can be cleaved and the cleavage residues removed from the film to yield a film where contact between NTs is unencumbered by dispersants, resulting in highly conductive NT films.

RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 61/471,582, filed Apr. 4, 2011, which is herebyincorporated by reference herein in its entirety, including any figures,tables, or drawings.

BACKGROUND OF INVENTION

Carbon nanotubes (NTs) have received significant attention fortechnological applications because of their desirable properties, whichinclude high electrical conductivity, high carrier mobility, and highmechanical strength; and due to their ability to be processed intovarious forms such as fibers and thin films. NTs in the form of networksand films have been proposed as electrodes for several types of devices,including: polymeric supercapacitors; transparent electrodes for organiclight emitting diodes and organic photovoltaic devices; and organicelectrodes for organic light emitting diodes, organic photovoltaicdevices, and organic electrochromic devices. NT dispersions within anelectroactive organic matrix, such as, poly(3-alkylthiophene)s andpoly(phenylene vinylene)s, have demonstrated a potential to act as anelectroactive component within a bulk heterojunction photovoltaicdevice. Recent work has demonstrated that dispersing NTs within anorganic polymeric matrix, such as polystyrene and a polyacrylate,dramatically increases its strength, toughness, and durability inaddition to its introduction and augmentation of other properties.Therefore, dispersion of NTs into electroactive organic materials ispromising as active sites of: charge storing supercapacitors/batteries;solar cells; electrochromic fiber and film-based devices; and lightemitting devices, which, aside from producing enhanced electronicproperties, can result in durable and robust materials.

Critical to the commercial success of NT films is an ability to processthe films on a large scale via methods such as printing, roll-to-rollcoating, and spraying. Such processing methods require solutions orsuspensions of NTs that are well-dispersed and where the homogeneoussolution or suspension can be maintained for an extended period of time.Examples of such carbon NT dispersants include ionic and non-ionicsurfactants, DNA, conjugated polymers, and non-conjugated polymers thatcontain polycyclic aromatic groups, such as pyrene and porphyrins. NTfilms for high-end electronic applications require a low sheetresistance (<300 Ohms/sq) and, for those applications involvingtransparent electrodes, the low sheet resistance must be accompanied bya high transmittance (above 75%) of electromagnetic radiation in thewavelength region of interest. However, NT thin films that have beendeposited as dispersions, using techniques that are amenable to largescale production, have resulted in sub-optimal transparency and/orconductivity, usually with a resistivity above 1,000 Ohms/sq when havingacceptable transmittance levels. Many dispersants, especially polymericdispersants, have been designed to blend NTs into polymer composites asreinforcement materials but are not appropriate for the formation oftransparent conductive thin-film electrodes. Typically, NT dispersantsare irreversibly bound to the nanotubes, where the NT dispersant exceedsthe content of the NTs in the thin film and have not demonstrated thecapability for use in high-end electronic applications.

Therefore, a need remains for a NT dispersant that allows the formationof a stable dispersion of carbon NTs and that can be easily removed toform a thin film without damaging or detracting from the structure andproperties possible for NTs. Additionally, these dispersants would beuseful for formation of nanotube composite materials for electroactiveand related devices including: electroluminescent devices;photovoltaics; electrochromic films and fibers; field-effecttransistors; batteries; capacitors; and supercapacitors.

SUMMARY OF INVENTION

An embodiment of the invention is directed to a degradable polymericcarbon nanotube (NT) dispersant comprising a multiplicity of NTassociative groups coupled to a polymer backbone by linking groups andhaving a plurality of cleavable groups situated between NT associativegroups. In this manner, individual NT associative groups are separatedfrom other NT associative groups, where cleavage of the cleavable groupsleaves residual fragments from the polymeric carbon nanotube (NT)dispersant that have no more than one NT associative group. The NTassociative group comprises a polycyclic aromatic group capable of beingnon-covalently associated with a NT or other graphene structure. Thedegradable polymeric NT dispersant is soluble in at least one solvent.The cleavable groups comprise a functional group that can be cleaved bya change in temperature, a change in illumination, addition of one ormore chemicals, or any combination thereof by a cleavage reaction thatdoes not adversely change the NT film's structure. The linking groupcomprises 2 to about 20 single or multiple covalent bonds comprising achain of carbon atoms and, optionally, heteroatoms or a chain of siliconatoms and, optionally, heteroatoms. The polycyclic aromatic groupscomprise pyrene, anthracene, pentacene, benzo[a]pyrene, chrysene,coronene, corannulene, naphthacene, phenanthrene, triphenylene, ovalene,benzophenanthrene, perylene, benzo[ghi]perylene, antanthrene,pentaphene, picene, dibenzo[3,4;9,10]pyrene, benzo[3,4]pyrene,dibenzo[3,4;8,9]pyrene, dibenzo[3,4;6,7]pyrene, dibenzo[1,2;3,4]pyrene,naphto[2,3;3,4]pyrene, porphyrin derivatives, or any combinationthereof.

Another embodiment of the invention is directed to nanotube (NT)dispersions comprising a plurality of NTs or NT equivalents, adegradable polymeric NT dispersant, and a solvent in which the NTs aredispersed by the dissolved degradable polymeric NT dispersant. The NTsor NT equivalents can be single walled carbon nanotubes (SWNTs), doublewalled carbon nanotubes (DWNTs), multi walled carbon nanotubes (MWNTs),graphene sheets, or other graphene structures. The dispersion caninclude other nanoparticles or microparticles. In one embodiment of theinvention, the nanoparticles or microparticles can be a material that isnot dissolved in the solvent of the dispersion, but is soluble in asecond solvent.

Another embodiment of the invention is directed to a method of forming aNT comprising film, where a NT dispersion is deposited on a substrate,the cleavable groups of the degradable polymeric NT dispersant arecleaved, and the solvent and the cleavage residues from the degradablepolymeric NT dispersant are removed, although not necessarily in thesame step. Deposition can be carried out by air brushing, electrostaticspraying, ultrasonic spraying, ink-jet printing, roll-to-roll coating,or dip coating. Removal of the solvent can be carried out before orafter cleavage of the cleavable groups. Promoted cleavage can occur bythermolysis, photolysis, addition of a catalyst, addition of one or morereagents, addition of one or more solvents, or any combination thereof.Removing can be carried out by filtering, washing, or evaporating.

In an embodiment of the invention, a NT comprising film comprises amultiplicity of NTs free of residual dispersants having intimateelectrical contact between the NTs throughout the film, and thethickness of the film varies in a predetermined pattern, such as thickNT lines separating thin NT windows. The predetermined pattern can beformed by deposition of at least a portion of the film by one of thedeposition methods listed above. For example, the predetermined patterncan be a grid of NTs deposited by ink-jet printing on an approximatelyuniform thick transparent nanotube film substrate, where the depositedlines are thick relative to the film but have a small width such thatvery transparent windows of the substrate film are separated by the lesstransparent or opaque patterned grid. For example, the grid can have atransparency of less than 50% transmittance and the windows can have atransparency in excess of 75% transmittance such that the griddiminishes little of the apparent transparency of the film but improvesthe conductivity of the film relative to a uniformly thick film lackingthe grid.

These and other features and advantages of the present invention will beapparent for those skilled in the art. While numerous changes may bemade by those skilled in the art, such changes are within the spirit ofthe present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a reaction scheme for the homopolymerization of an acetalmonomer to form an organic solvent soluble degradable polymeric NTdispersant via an ADMET polymerization, according to an embodiment ofthe invention, and reduction of the ADMET formed ene comprising polymerto a saturated polymer, according to an embodiment of the invention.

FIG. 2 shows a reaction scheme for the formation of a monomer and itssubsequent polymerization to a degradable polymeric NT dispersant viaalkoxysilane formation, according to an embodiment of the invention.

FIG. 3 shows a reaction scheme for the formation of a degradablepolymeric NT dispersant with enhanced organic solvent solubility via anADMET copolymerization, according to an embodiment of the invention.

FIG. 4 shows a reaction scheme for the formation of a water solubledegradable polymeric NT dispersant via an ADMET copolymerization,according to an embodiment of the invention.

FIG. 5 shows a reaction scheme for the synthesis of an acetal monomerfor the preparation of a degradable polymeric NT dispersant via an ADMETpolymerization, according to embodiments of the invention.

FIG. 6 shows a reaction scheme for the synthesis of an.alpha.,.omega.-diene monomer for copolymerization with an acetalmonomer for the preparation of a degradable polymeric NT dispersant withenhanced organic solvent solubility via an ADMET copolymerization,according to embodiments of the invention.

FIG. 7 is a Visible-NIR spectrum of a 60 to 65 nm thick NT comprisingfilm prepared by acid catalyzed degradation of cleavable groups in thelinking group between a pyrene associative group and a hydroxypropylcellulose NT dispersant where the film was deposited by spraying a NTdispersion onto a glass substrate, according to an embodiment of theinvention.

FIG. 8 is a plot of the sheet resistance over time of the NT film havingthe visible-NIR spectrum of FIG. 7.

DETAILED DESCRIPTION

Embodiments of the invention are directed to an on demand degradablepolymeric dispersant for carbon nanotubes (NTs) having a multiplicity ofNT associative groups where the dispersant can be removed afterformation of a film or other structure by a degradation of thedispersant to individual, monomeric, associative groups that remainafter cleavage from the polymer. The associative groups can bepolycyclic aromatic units, such as a pyrene units. The NT associativegroups bind strongly to the NTs in a cooperative manner when linked viathe polymer, where binding of multiple individual NT associative groupskeep the NT coupled to the polymers independently of the association ordissociation of any individual NT associative group with the NT. Uponcleavage of cleavable groups, the NT associative groups dissociate fromthe polymers, allowing the monomeric NT associative groups to undergo anassociative/dissociative equilibrium that can be driven to thedissociative form and allow the removal of the NT associative groupsfrom the NTs, which also allows the residual cleaved coupling polymerportion of the polymeric dispersant to be removed from an electrode orany other device comprising the NT film or other NT equivalentstructure.

In another embodiment of the invention, a dispersion of NTs, preparedfrom NTs and the degradable polymeric NT dispersants, is formed that canbe used as an ink to form highly conductive printed films of NTs.Printed NT films, according to an embodiment of the invention, can beformed upon removal of the polymeric dispersant that are highlyconductive films, which can vary in thickness and transparency over thearea of the film, as permitted by the deposition method employed. Forexample, the printed film can comprise a grid of continuous highlyconductive bands of NTs having relatively low transparency framingwindows of NTs that are highly transparent, where the conductivity ofthe windows is high, but lower than that of the bands of the grid. Theprinted nanotube films can be doped to further enhance theirconductivity. Doping can be conducted by any method known in the art andthe dopant can be any material known to dope NTs, including, but notlimited to: halogens; sulfuric acid; alkali metals; quinones; boranes;bora-tetraazapentalenes; aminium or ammonium salts; sulfonium salts;oxonium salts; selenonium salts; nitrosonium salts; arsonium salts;phosphonium salts; iodonium salts; select metal (e.g. silver) salts; andphotoacids, such as di- or multi-aryl sulfonium and iodonium salts.

In an embodiment of the invention, the degradable polymeric NTdispersants comprise a polymer backbone and a pendant group thatcomprises a polycyclic aromatic group that binds strongly, yetreversibly, to the wall of a carbon NT or other graphene surface, forexample, a graphene sheet. The pendant group is attached to repeatingunits of the polymer backbone and, in some cases, to the ends of apolymer in addition to non-terminal repeating unit of the polymer. Thependant group can be attached to a terminal or non-terminal repeatingunits of the polymer. The polymer can be a linear, branched,hyperbranched, or dendritic polymer. The polymer can be a homopolymer ora copolymer of two or more different repeating units. The polymer, whichcan be a copolymer having a plurality of different repeating units, canbe any polymer that can be prepared by a step-growth or a chain-growthpolymerization, including, but not limited to: polyamides; polyesters;polycarbonates; polyimides; polybutadiene or other non-conjugatedpolyenes; and polysiloxanes. The polymer may be of natural origin, suchas those developed from cellulose. In embodiments of the invention, thepolymer backbone comprises heterostructures, such as heteroatoms orcarbons having different hybridization, such as isolated ene units,where the polymer backbone can be degraded to facilitate removal offragments from the polymer other than the fragments that contain asingle NT associative group. In an embodiment of the invention, havingformed degradable polymeric NT dispersants of one polymer structure,reaction can be carried out on the polymer to form another structure, ascan be appreciated by those skilled in the art and illustrated in theexemplary embodiment shown in FIG. 1 for the reduction of anon-conjugated polyene. The degradable polymeric NT dispersants aresoluble in at least one solvent when the NT associative groups areattached to the polymer, and the degradation residues, either polymeric,oligomeric, or monomeric species, are soluble in the same or a differentsolvent. In embodiments of the invention, the polymer can be of lowdegree of polymerization, for example a trimer, tetramer or even adimer, and can be referred to as an oligomer or as a polymer. One ormore of the NT associative groups can be attached to an end-group of thepolymer.

The NT associative groups are attached to a repeating unit of thepolymer via a linking group that comprises 2 to about 20 covalent bondsthat are either single or multiple bonds. The linking group can be achain of carbon atoms or combination of carbon atoms and heteroatoms,including, but not restricted to: oxygen; nitrogen; silicon;phosphorous; and sulfur. In another embodiment of the invention, thelinking group can comprise a chain of 2 to about 20 covalent bondsbetween silicon atoms or between silicon atoms with heteroatoms,including, but not restricted to: oxygen; nitrogen; and carbon. In oneembodiment of the invention, the linking group comprises 6 to 20covalent bonds, permitting the decoupling of the polymer backbone'sconformation from the NT associative groups binding to the NTs. Thecleavable bonds that permit degradation can reside within the polymerbackbone or the linking groups. To assure degradability to fragmentshaving only a single NT associative group, the degradable polymeric NTdispersant, according to an embodiment of the invention, has no morethan one pendant NT associative group residing on a given repeating unitand the disposition of cleavable bonds is such that only one NTassociative group can reside in a degradation fragment after completedegradation of the degradable polymeric NT dispersant by cleavage of allcleavable groups.

NT dispersants used to prepare NT dispersions can have cleavable groupson the pendant groups. A plurality of NT associative groups on adegradable polymeric dispersant can be coupled to a single repeatingunit as long as cleavage of all cleavable bonds results in thegeneration of degradation residues that contain no more than a single NTassociative group, where, in this manner, a NT film can form that iseffectively free of residual fragments from the NT dispersant. This typeof NT dispersant has at least one cleavable group on the linking groupor groups per NT associative group attached to the linking group. In anembodiment of the invention, a method of forming a NT film requiresdegradation with a very high cleavage efficiency, such that uponreaction no pair of NT associative groups remains coupled in a singlemolecule. Cleavage results in degradation fragments with a single NTassociative group.

Although the monomeric NT associative groups can bind to the NTs, thelack of cooperation between a plurality of molecularly coupled NTassociative groups after degradation allows their effective removal.This removal allows the remaining NTs to have intimate contact betweentwo unhindered adjacent NTs at, on average, a plurality of sites alongany given NT, allowing electrical percolation within the film that givesrise to high conductivities of the NT films. Any NT associative group onthe non-degraded polymeric NT dispersant that dissociates from the NT isobliged to remain in the immediate proximity of the NT because of thecooperative binding of a NT with a multiplicity of NT associative groupslinked to the same degradable polymeric NT dispersant. An equilibriumstate is established with the NT strongly binds to the degradable NTdispersant due to this cooperative binding of a multiplicity of NTassociative groups. The decoupled monomeric NT associative groups candiffuse from the NT after degradation of the polymer and/or linkinggroups and the associative-dissociative equilibrium between thatmonomeric NT associative group and the NT can be driven to effectivelycompletely dissociate and remove the NT associative groups. For example,multiple washings with a solvent or solution that has an affinity forthe monomeric NT associative groups, results in removal of the NTassociate groups from a NT film. Effectively, complete dissociation canbe considered to occur when a sufficient amount of NT associative groupsand other polymeric residues are removed to an extent that every NT canmake unhindered contact to at least one other NT, such that the averagesized NT has a plurality of contacts within the resulting matrix of afilm or other structure. Although absolute removal of all monomeric NTassociative groups containing residue from the degradable polymeric NTdispersant is not required, the effectively complete removal will occurin most systems.

In another embodiment of the invention, multiple depositions of NTs canbe made on a substrate to form a film or a patterned film, where atleast one of the depositions employs a NT dispersion employing one ormore degradable polymeric NT dispersants. After degradation of thedegradable polymeric NT dispersants, the monomeric NT associative groupscan diffuse to portions of the multiply-deposited film that iseffectively free of NT associative groups. For example, a portion of thefilm that was effectively free of NT associative groups, a portionhaving no NT associative attached in a manner that disrupts electricalconnectivity between NTs, can bind with monomeric NT associative groupsreleased from other portions of the film having monomeric NT associativegroups in a manner where disruption of existing NT to NT contact doesnot occur. For example, a NT film according to U.S. Pat. No. 7,776,444,incorporated herein by reference, is a NT associative group free filmthat can be used as a substrate upon which a patterned NT film is formedby deposition of a degradable NT dispersion using a printing method,which, upon degradation of the NT dispersant on the patterned film, thefragments with monomeric NT associative groups can migrate to thesubstrate NT film without disrupting the NT to NT association of thesubstrate NT film.

When used to form a nanotube dispersion, the associative group of thepolymeric associative dispersant can be a polycyclic aromatic group thatcan non-covalently bind to the sidewalls of a carbon NT throughpi-stacking. Other non-covalent associative forces can be used to bindwith the carbon nanotubes. Unlike covalent bonding, the binding betweenan associative group and a NT does not disrupt the nanotube structure ina manner that alters or compromises the nanotubes' properties that arederived from the delocalized pi-system. As used herein, the carbon NTsinclude: single wall nanotubes (SWNTs); multiwall nanotubes (MWNTs); orNT equivalents, including graphene sheets, other graphene structures, orany mixtures comprising NTs and/or NT equivalents.

In an embodiment of the invention, a variety of polycyclic aromaticgroups can be used as associative groups of the degradable polymeric NTdispersants. Any one of these polycyclic aromatic groups can be usedexclusively or in combination with one or more other structurallydifferent polycyclic aromatic groups as the associative groups of thedegradable polymeric NT dispersant. Examples of the polycyclic aromaticgroups that can be used for non-covalent binding associative groupsinclude, but are not limited to: pyrene; anthracene; pentacene;benzo[a]pyrene; chrysene; coronene; corannulene; naphthacene;phenanthrene; triphenylene; ovalene; benzophenanthrene; perylene;benzo[ghi]perylene; antanthrene; pentaphene; picene;dibenzo[3,4;9,10]pyrene; benzo[3,4]pyrene; dibenzo[3,4;8,9]pyrene;dibenzo[3,4;6,7]pyrene; dibenzo[1,2;3,4]pyrene; naphto[2,3;3,4]pyrene;and porphyrin derivatives. A polycyclic aromatic associative group canbe linked to: every repeating unit of the polymer; alternating repeatingunits of the polymer; or randomly or regularly linked to three or morerepeat units of a polymer. A NT associative group can be linked to oneor more terminal ends of the degradable polymeric NT dispersant.

Embodiments of the invention are directed to the preparation ofdegradable polymeric NT dispersants. Monomeric units that comprise alinked NT associative group may be homopolymerized, as shown forexemplary embodiments in FIGS. 1 and 2, or copolymerized, as shown forexemplary embodiments in FIGS. 3 and 4, by any suitable mechanismincluding, but not limited to: polycondensation; ring-opening additionpolymerization; free radical addition polymerization; anionic additionpolymerization; cationic addition polymerization; coordinativering-opening addition polymerizations; step-growth or chain growthmetathesis polymerization; or any other suitable process. The degradablepolymer backbone may also be of natural origin, such as those based oncellulose. The structure of the polymeric chain can vary: to accommodatea desired process for using the degradable polymer NT dispersion; toallow deposition of a resulting NT film on a chosen substrate; toachieve desired conditions for deposition; or other considerations. Thepolymer of the degradable polymer NT dispersant can be water soluble oran organic solvent soluble polymer. The organic solvent can vary and canbe a non-polar solvent, such as an aliphatic or aromatic hydrocarbon, apolar aprotic organic solvent, such as tetrahydrofuran or acetone, or apolar protic solvent, such as an alcohol or a diol.

In an embodiment of the invention, the cleavable groups can residewithin the backbone within or between every repeating unit containing aNT associative group. Additional cleavable groups can be situated atregular or irregular position within the backbone. In another embodimentof the invention, the cleavage group resides in the linking groupbetween a polymer backbone and a NT associative group. The cleavablegroup can be any group where the group is stable for preparation anddeposition of a NT dispersion, but where conditions can be changed topromote cleavage of the group. The change of conditions can be: a changein temperature; illumination; addition of one or more chemicals that actas a catalyst and/or reagent; addition of a catalyst and additionalsolvent; or any combination thereof. For example, the cleavage can bedue to a thermolytic or photolytic bond breading reaction of thecleavable group, for example, a retro Diels-Alder reaction. The cleavagecan be promoted by a catalyst, for example, an acid or base thatpromotes a solvolysis reaction. The change in conditions can be appliedto a film formed from the NT dispersion. In an embodiment of theinvention, the change in conditions can include a change of solvent or achange of the solvent concentration that was used for the dispersionwith inclusion of a catalyst, such that the polymeric NT dispersion canbe in equilibrium with monomers or oligomers, for example, cyclicoligomers, where the proportion of NT associative groups containingrepeating units to total repeating units is sufficiently small and canessentially leave only oligomers containing a single NT associativegroup per oligomer.

For example, in an exemplary embodiment of the invention, the cleavablegroup is an acetal or ketal that resides within a repeating unit and/orin the linking group to the NT associative group of the degradablepolymeric NT dispersant. The NT dispersion formed from this degradablepolymeric NT dispersant can be used to form a film and an acidic orbasic catalyst can be added. For example, water or an alcohol solventwetting film is a reagent that results in the cleavage of an acetal orketal cleavable group. The added acid or base catalyst can be anyBronsted-Lowry or Lewis acid or base. Cleavage liberates monomericassociative groups and allows the simultaneous or sequential removal ofthe polymeric backbone portion or fragments of the polymeric backboneportion from the polymeric NT dispersant. The monomeric NT associativeunits may include a portion of the linking group, may include the entirelinking group, or may include a portion of the polymer backbone that canbe removed simultaneously or sequentially from other residue generatedupon cleavage. In another exemplary embodiment of the invention, thecleavable group can be a di-, tri- or tetra-alkoxysilane (silyl ester),or di-, tri- or tetra-silazane where the solvent or polymeric NTdispersant lacks an oxygen nucleophile, such that the alkoxy silane orsilazane can undergo subsequent hydrolysis or alcoholysis to liberatemonomeric NT associative groups from the polymer backbone, or residuesof the polymer backbone, by exposure of the film from the NT dispersionto the nucleophilic oxygen reagent and any appropriate catalyst that isrequired. In another exemplary embodiment of the invention, thecleavable group can be contained in the backbone of a polymer of naturalorigin, such as cellulose. According to embodiments of the invention,cleavage is carried out after the nanotube dispersion is deposited as afilm and where the cleavage reaction results in little disruption of theNT film structure such that any NT associative group free NT comprisingfilm becomes highly conductive yet of about an equivalent thickness tothe film deposited before removal of the NT dispersant. To assureeffective contacting of cleavable groups on NT film bound NTdispersants, degradation catalysts that are of a very large molecularweight or are solids are avoided. Therefore polymer bound reagents,enzymes or solid insoluble catalysts are not used to promote cleavage.

In embodiments of the invention, a NT dispersion comprising a liquidvehicle for fluidity, the degradable polymeric NT dispersant, and NTs isformed by the combination of the degradable polymeric NT dispersant,NTs, and a liquid, often referred to as “solvent” herein. The solventmay not truly dissolve the NT dispersions but does dissolve thedegradable polymeric NT dispersant when free of the NTs. Due to thecooperative nature of the polymeric NT associative groups, it ispossible, in some embodiments of the invention, that the degradablepolymeric NT dispersants can be employed in quantities where a singlemonolayer of the dispersant or even a sub-monolayer of the dispersant ona NT is sufficient to achieve a relatively stable dispersion. The NTscan be single wall nanotubes (SWNTs), multiwall nanotubes (MWNTs), or NTequivalents, such as a graphene sheets or other graphene structures. ANT dispersion can further comprise other nano, micro, or even largerparticles that can modify, as desired, the structure or properties of afilm or other structural matrix not primarily defined by two dimensions,where the structure is significantly smaller in thickness, a thirddimension. The additional particles can modify the ultimate propertiesof the resulting film or structural matrix. For example, in oneembodiment of the invention, metallic nanowires or nanoparticles can beincluded, where a second dispersant as needed or even sufficientmechanical agitation can be employed to achieve a sufficiently dispersedstructure. In another embodiment of the invention, polymericnanoparticles or microparticles that comprise any shape or mixture ofshapes, for example, sphere, rod, or disc, can be included in the NTdispersion. The polymeric nanoparticles can be employed in the finalstructure, or can be removed by dissolving in a solvent that is not theliquid vehicle used for the dispersion.

In other embodiments of the invention, the NT dispersants used to form aNT film can have a plurality of NT associative groups, as definedpreviously, attached via a linking group, as defined previously, to asingle repeating unit of a polymer, and where the cleavable group, asdefined previously, resides in the linking group. Although suchdispersants are potentially problematic for the degradation processbecause of potential steric inhibition of the cleavage reaction by theassociated NT, such NT dispersants can be used when the cleavable groupis symmetric, for example, a flat ester group or an ene, where the NTassociative group cannot oblige a preferred face of the cleavable groupto be shielded by the NT to which it is associated. Again, solid or highmolecular weight catalysts or reagents are avoided for the cleavagereaction to promote cleavage of all cleavable bonds and achieve easyremoval of fragments comprising a single NT associative group. Forexample a pyrene-containing hydroxypropyl cellulose derivative (HPC-Py)as disclosed in Yang et al. Ind. Eng. Chem. Res. 2010, 49, 2747-51,incorporated by reference herein, can be employed as the NT dispersant,although the disclosed method of cleavage by an enzyme must be avoidedas Yang et al suggests that an enzyme was incapable of generatingmonomeric NT associative cleavage fragments even when the NT dispersionis not deposited as a film.

The NT dispersion can be applied to a surface of any material. In anembodiment of the invention, the NT dispersion can be applied to asurface that can be: a transparent or opaque material; a resistant,semiconductive, or conductive material; or a soluble or insolublematerial. For example the surface can be the surface of a plastic,glass, ceramic, semiconductor, or metal. The surface can be flat or havedifferent elevations relative to a hypothetical flat base, and can beconsidered smooth or rough at dimensions that are small relative tothose of any pair of defined elevations. In an embodiment of theinvention, the NT dispersion is applied to the surface by any brushing,spraying, printing or coating process. For example air brushing,electrostatic spraying, ultrasonic spraying, ink-jet printing,roll-to-roll coating, rod coating, or dip coating can be employed todeposit a film. The liquid vehicle can be removed to leave a filmcomprising the NTs associated to the degradable polymeric NT dispersantand the environment of this film modified to promote cleavage reactionsthat leave a film comprising NTs but is not associated to any NTassociative groups that are not monomeric in nature. The residualdegradation products can be removed from the NT comprising film bywashing and/or evaporating the degradation products and liquids employedfor the steps of deposition, degradation, or removal.

The NT dispersion can be deposited, for example, by spraying onto asubstrate, where the liquid vehicle is a single solvent or a mixture ofsolvents that is compatible with the substrate. It is desirable that theNT dispersion exhibits stability for at least several hours, days, orweeks for production of a NT comprising film in a mode where reservoirsfeeding a sprayer, printer or coater or a bath for dip coating the filmon a substrate need not be immediately prepared prior to deposition. TheNT dispersant is then removed from the NTs in a manner that does notdamage the nanotubes or the supporting substrate, and does notde-laminate the nanotubes from the substrate. For example, if removalrequires heating, the heating is carried out in a controlled manner toavoid formation of voids due to rapid expansive loss of gaseousproducts. Decomposing and/or depolymerizing the NT dispersant should becarried out under conditions that do not promote reactions involvingbonds of the NTs. Decomposition can be carried out chemically upon:introduction of a catalyst and/or reagent, for example, a dilute acidicor basic solution; illumination, for example, from a coherent orincoherent light source at visible or ultraviolet portions of theelectromagnetic spectrum; or heating to cause thermal decomposition, forexample, in an oven with controlled heating and pressure. Removal of thedecomposition products can involve washing or vaporizing to leave a NTdispersant free conductive NT film. Because the decomposition andremoval have been carried out without generation of voids, pores, orgaps, intimate nanotube to nanotube contact can be maintained or formand yield the desired dispersant free low sheet resistance NT comprisingfilm.

In one exemplary embodiment of the invention, NTs are suspended in waterusing a surfactant, such as, but not limited to, Triton-X 100, and theNT dispersant in solution is added to the NT suspension to form the NTdispersion. The solvent can be water, a water soluble solvent, or awater insoluble solvent. Upon mixing, the NT dispersant displaces someor all of the surfactant at the NT surface due to the superior NTbinding affinity of the NT dispersant's NT associative group, which isfurther promoted by the multiplicity of NT associative groups. Asneeded, the suspension can be heated in a controlled manner, or areagent can be added that has a higher affinity for the surfactant thanthe NTs but has lesser affinity for the NT dispersant than does the NTs.The NT dispersion formed upon mixing is subsequently filtered and washedto remove surfactant and any free excess NT dispersant; leaving the NTdispersion in a form for application to a substrate upon addition of thedesired solvent or solvent mixture to the NT dispersion, generally, butnot necessarily, with agitation.

In another embodiment of the invention, NTs that are suspended in waterusing a surfactant are filtered and washed with water to remove excesssurfactant to leave a NT film where the NTs are not deposited with anyimposed orientation within the plane of the filter. NT dispersions canbe formed by addition of a desired solvent and a polymeric NT dispersantto the NT film without drying the film or after drying the film. Theformation of the NT dispersion can be promoted by stirring at aprescribed temperature or a profile of increasing and/or decreasingtemperatures, and possibly refluxing the solvent under an air or inertatmosphere, for example, an argon or nitrogen atmosphere.

In an embodiment of the invention, the films can be deposited such thatthe NTs are homogeneously dispersed over the surface to which they aredeposited. In another embodiment of the invention, a pattern of NTs canbe formed when employing appropriate deposition techniques, such asprinting, or by a series of depositions of NT films where the area ofdeposition can be controlled over the area to a sufficient tolerance. Inthis manner, according to an embodiment of the invention, a patternedfilm can have varied thickness over the area of the surface of the filmin a predetermined fashion. For example, a series of lines or a grid ofNT comprising lines, which are thin in the plane of the film but arerelatively thick perpendicular to the plane, can be used to connectcontinuous thin transparent NT comprising windows, such that the NTcomprising lines are very highly conductive but are of low transparencyor are opaque. In this manner the NT comprising lines electricallyconnect very transparent NT comprising windows of lower conductivitysuch that the overall conductivity is very high but where the overallloss of transparency over the entire grid is low relative to the samemass of NTs dispersed evenly over the entire film's surface. As can beappreciated by those skilled in the art, the deposition can employ anymethod where the NT dispersion can be placed on a specific area at aspecific concentration, or where a specific area can be over printed oneor more times to achieve a desired profile of NT film thicknesses, forexample, by using the NT dispersion as a NT ink for printing thepatterned film. For example, a grid of lines of low transmittance NTs,for example, less than 50% transmittance, can be printed over a firstdeposited homogeneous thin NT film such that the printed lines accountfor less than 10 percent of the area of the film and contact theunderlying thin film to form windows of NTs having greater than 85%transmittance that account for more than 90% of the area of the film,where the resulting patterned film displays an improved conductivity andtransparency relative to a uniformly thick homogeneous film of the samemass of nanotubes.

Materials and Methods Preparation of 6-bromohexan-1-ol

To carry out the first transformation shown in FIG. 5, hexan-1,6-diol(60 g, 0.25 mol) was added to a 1 L 3-necked flask and placed under anitrogen atmosphere. To this flask was added toluene (600 mL) andconcentrated HBr (66 mL of a 48% (9M) aqueous solution). The mixture washeated under reflux for a period of 36 hours using thin layerchromatography (TLC) to monitor conversion. After cooling the reactionmixture to room temperature, two separate phases formed. The organicphase was diluted with diethyl ether and washed with 1 M NaOH and brine.The organic portions were isolated and dried using anhydrous magnesiumsulphate. Removal of the solvent in vacuo resulted in a yellow oil thatwas distilled under vacuum at 110-120.degree. C. to yield 38 g (84%yield) of 8-bromooctan-1-ol.

Preparation of 2-(6-bromohexyloxy)tetrahydro-2H-pyran

To carry out the second transformation shown in FIG. 5,8-bromooctan-1-ol (20.00 g, 0.096 mol) was transferred to a 1 L 3-neckedflask and placed under a nitrogen atmosphere and dissolved in 200 mL ofdegassed diethyl ether. Ferric perchlorate (1.06 g, 3.times.10.sup.-3mol) and 2,3-dihydropyran (THP) (12.09 g, 0.144 mol) were added to theflask. The mixture was stirred at room temperature for 1.5 hours, withthe reaction progress followed by TLC. The reaction mixture was passedthrough a short column of silica gel using petroleum ether as eluent.The solvent was evaporated to dryness to afford 22.23 g (87% yield) of2-(6-bromohexyloxy)tetrahydro-2H-pyran.

Preparation of (6-((tetrahydro-2H-pyran-2-yl)oxy)hexyl)magnesium bromide

To carry out the third transformation shown in FIG. 5, a 500 mL,3-necked flask was dried overnight in an oven and charged with 10.00 g(416 mmol) of magnesium turnings and a magnetic stirrer bar. Themagnesium was dried under a rapid stream of argon while heated by a heatgun. After cooling to room temperature, the rate of argon flow wasreduced and 200 ml of anhydrous nitrogen degassed diethyl ether wasadded via a syringe to the reaction vessel. To the reaction vessel wasslowly added 10 mL of argon degassed 1,2-dibromoethane. The mixture wasstirred at room temperature for one hour followed by stirring at refluxfor an additional 1 hour, where ether reflux resulted from theexothermic reaction with the eroding magnesium surface. A small crystalof iodine was added to the vessel. A clear black solution resulted whichdecolored after reflux for an hour. A solution of 10.00 g (37.72 mmol)of 2-((6-bromohexyl)oxy)tetrahydro-2H-pyran in 20 mL of anhydrous THFwas added drop wise via syringe. After complete addition, the mixturewas refluxed for two hours to form a Grignard reagent solution.

Preparation of2-((6-(5a.sup.1,8a-dihydropyren-1-yl)hexyl)oxy)tetrahydro-2H-pyran

To carry out the fourth transformation shown in FIG. 5, 10 g (35.60mmol) of 1-bromopyrene and 0.2 g (1 mmol) of1,2-bis(diphenylphosphino)ethane nickel(II) chloride were dissolved in150 mL of anhydrous diethyl ether and the mixture brought to reflux. TheGrignard reagent solution was transferred via syringe to the reactionvessel. The reaction mixture was heated under reflux for two hours.After cooling to room temperature, the reaction was poured intodeionized water and extracted using dichloromethane. The isolatedorganic solution was dried using magnesium sulphate. Pure pyrene THPether, 9.42 g (68% yield), was obtained by column chromatograph using a1:1 dichloromenthane:hexane mixture followed by removal of the solvent.

Preparation of 6-(5a.sup.1,8a-dihydropyren-1-yl)hexan-1-ol

To carry out the fifth transformation shown in FIG. 5, a mixture of 5.78g (14.90 mmol) of the pyrene THP ether and 0.40 g (1.12 mmol) ofFe(ClO.sub.4).sub.3 were stirred in 80 mL of a equivolume mixture ofMeOH and Toluene at 50.degree. C. for 12 hours with progress of thereaction monitored by TLC. After completion of the reaction, thesolvents were evaporated in vacuo and 4.15 g, (92% yield) of the purepyrene alcohol was isolated by column chromatography usingdichloromethane as solvent after evaporation of the solvent.

Preparation of 6-(5a.sup.1,8a-dihydropyren-1-yl)hexanal

To carry out the sixth transformation shown in FIG. 5, 20 mL of aanhydrous dichloromethane was transferred to a 3 neck round bottom flaskunder argon and cooled to −78.degree. C. using a dry ice/acetone bathand 1.71 mL (24.1 mmol) of dimethylsulfoxide was added. Via a syringe,1.39 mL (16.2 mmol) of oxalyl chloride was added dropwise into thevessel and the mixture was stirred for 30 minutes. A solution of 2.41 g(7.89 mmol) of the pyrene alcohol in 50 mL of dichloromethane was addeddropwise to the mixture over 5 minutes. The resulting highly viscousmixture was stirred for 40 minutes at −78.degree. C. and 10 mL ofanhydrous triethylamine was added slowly. The yellow mixture was warmedto room temperature, diluted with 150 mL of dichloromethane, and washedthree times with 50 mL of water. The organic layer was collected anddried using magnesium sulphate. After evaporation of the solvents, 1.89g (80% yield) of a solid white pyrene aldehyde product was isolated.

Preparation of6-(6,6-bis(hex-5-en-1-yloxy)hexyl)-3a,3a.sup.1-dihydropyrene

To carry out the final transformation shown in FIG. 5, 2.00 g, (6.66mmol) pyrene aldehyde was transferred to a 100 mL three neck roundbottomed flask under an argon atmosphere and dissolved in 40 mL of drytetrahydrofuran. To the flask was added 2.92 g (26.6 mmol) 5-hexen-1-oland 0.92 g (6.7 mmol) of HO.sub.3S—SiO.sub.2. Preparation of theHO.sub.3S—SiO.sub.2 is given below. The mixture was refluxed under theargon atmosphere for 24 hours. Solvent was evaporated from the mixtureand the resulting yellow oil was heated under vacuum at 50.degree. C. toremove residual 5-hexen-1-ol. The acetal monomer was isolated usingcolumn chromatography employing a 1:1 dichloromethane:hexane mixture.

The HO.sub.3S—SiO.sub.2 supported acid catalyst was prepared in thefollowing manner. To a solution of 20 mL of ethanol and 15 mL ofdeionized water was added 9.33 g (44.8 mmol) of tetraethylorthosilicate(Si(OEt).sub.4) and 0.84 g (3.6 mmol) of3-mercaptopropyltriethoxysilane. The mixture was stirred for 2 hours atreflux. A wet gel was separated from the liquid by evaporation in vacuoand isolated as a white solid. The gel was transferred to a 100 ml3-neck round bottom flask, to which 30 mL of acetonitrile andsubsequently 5 mL of 31% aqueous hydrogen peroxide solution were added.The mixture was heated to reflux for a period of six hours. Theresulting white gel was filtered and washed with deionized water andsubsequently with ethanol. After drying in vacuo for about 30 minutes,the white solid gel was transferred to a 500 ml round bottom flask and100 mL of aqueous 0.1 M sulfuric acid was added. The mixture was stirredfor one hour. The solid was filtered and washed with deionized wateruntil the resulting slurry displayed a neutral pH. The solidHO.sub.3S—SiO.sub.2 supported acid catalyst was isolated and dried in avacuum oven at 100.degree. C. for 6 hours before use.

Homopolymerization of6-(6,6-bis(hex-5-en-1-yloxy)hexyl)-3a,3a.sup.1-dihydropyrene

Prior to polymerization as shown in FIG. 1, 100 mg (0.20 mmol) of theacetal monomer was dried under vacuum at 50.degree. C. for 12 hours,dissolved in 0.5 mL of degassed dichlorobenzene, and the monomersolution was degassed with argon for one hour. The monomer solution wastransferred using a cannula to a Schlenk tube containing 1.65 mg(2.01.times.10.sup.-3 mmol) of Grubbs' 1.sup.st generation catalyst (1mol %) that had been dried under vacuum overnight. The polymerizationmixture was stirred under a vacuum of 70 Torr at 45.degree. C. for fourdays. The reaction was quenched by addition of 1 mL of ethyl vinyl etherin 5 mL of dichlorobenzene and the polymer was isolated as a gum byprecipitation in non-acidic methanol to remove catalyst residue and anyunconverted monomer.

Preparation of 2,5-dibromobenzene-1,4-diol

To carry out the first transformation shown in FIG. 6, a solution of90.61 g (0.57 mol) of bromine in 20 mL of glacial acetic acid was addeddropwise over three hours to a stirred suspension of 30 g (0.27 mol)hydroquinone in 200 mL of glacial acetic acid at room temperature. Thestirred reaction mixture displayed a mild exotherm with the temperaturerising to approximately 30.degree. C. which was accompanied by theformation of a clear solution followed by precipitation of a colorlesssolid after 5-10 minutes. Stirring was continued overnight. The solidwas isolated by filtration and washed with a small amount of glacialacetic acid. The filtrate was concentrated in vacuo to about half itsoriginal volume and chilled for 30 minutes. The solid was washed withhexanes to remove residual acetic acid to yield 39.35 g (55%) of2,5-dibromobenzene-1,4-diol.

Preparation of 1,4-dibromo-2,5-bis((2-ethylhexyl)oxy)benzene

To carry out the second transformation shown in FIG. 6, a suspension of28.34 g (0.11 mol) or 2,5-dibromobenzene-1,4-diol, 40.91 g (0.13 mol) of2-ethylhexylbromide, and 58.56 g (0.42 mol) of potassium carbonate in500 mL of acetonitrile was heated to reflex for 48 hours under nitrogen.The mixture was poured into 500 mL of deionised water and the resultingsuspension was filtered using celite and dissolved in dichloromethane.Removal of the solvent resulted in a residual dark brown oil. The oilwas dissolved in hexane and purified via column chromatography. Thesolvent was removed under reduced pressure leaving a clear oil. The oilcontained residual 2-ethylhexyl bromide, which was removed by vacuumdistillation using a Kuglerohr at 70.degree. C. for two hours to give32.87 g (61% yield) of 1,4-dibromo-2,5-bis((2-ethylhexyl)oxy)benzene.

Preparation of1,4-bis((2-ethylhexyl)oxy)-2,5-di(undec-10-en-1-yl)benzene

To carry out the final transformation shown in FIG. 6, 1.00 g (2 mmol)of 1,4-dibromo-2,5-bis((2-ethylhexyl)oxy)benzene was placed in a 250 mL3-neck round bottomed flask and 20 mL of anhydrous tetrahydrofuran wasadded under an argon atmosphere. The resulting solution was cooled to−78.degree. C. using a dry ice and acetone bath. Using a syringe, 2.17mL of a 2.3 M n-BuLi in hexane (5 mmol n-BuLi) was added dropwise andthe mixture was stirred for 30 minutes. To the mixture, 1.39 g (6 mmol)of 11-bromoundec-1-ene dissolved in 5 mL of tetrahydrofuran was addeddropwise using a syringe. The mixture was stirred overnight at roomtemperature. The mixture was poured into de-ionised water and extractedwith dichloromethane. The organic portions were combined and dried withanhydrous magnesium sulfate.

Random Copolymerization of6-(6,6-bis(hex-5-en-1-yloxy)hexyl)-3a,3a.sup.1-dihydropyrene with1,4-bis((2-ethylhexyl)oxy)-2,5-di(undec-10-en-1-yl)benzene

As shown in FIG. 3, a mixture of 1.00 g (2.07 mmol) of6-(6,6-bis(hex-5-en-1-yloxy)hexyl)-3a,3a.sup.1-dihydropyrene and 1.32 g(2.07 mmol) of1,4-bis((2-ethylhexyl)oxy)-2,5-di(undec-10-en-1-yl)benzene was driedunder vacuum for 48 hours and transferred to a Schlenk tube equippedwith a magnetic stirring bar under an argon atmosphere. A 5.67 mg(0.0069 mmol) quantity of Grubbs' 1.sup.st generation catalyst wastransferred to the tube to form a 300/1 monomer/catalyst mixture thatwas stirred under vacuum at 45.degree. C. for four days. As shown inFIG. 4, the polymerization reaction was quenched by addition of 10 mLethyl vinyl ether, and the copolymer was precipitated by addition toacidic methanol and isolated as an adhesive gum upon removal of themethanol solution.

Pyrene substituted hydroxypropylcellulose (HPC-Py) was mixed with asuspension of SWNTs in water, where the monomeric surfactant Triton-X100 (Polyethylene glycol mono [4-(1,1,3,3-tetramethylbutyl)phenyl]ether) was use to form the NT suspension. The suspension wasfiltered and washed to remove the Triton-X 100 liberated upon additionof the HPC-Py. Various NT-HPC-Py dispersions were prepared by theaddition of water, ethanol, or an ethanol/water mixture. The ethanolNT-HPC-Py dispersion was sprayed uniformly on a glass substrate and theresulting film was warmed to 80.degree. C. to evaporate the ethanol. Theresulting film was deposited on the glass with no apparent voids. TheHPC-Py was decomposed by placing a 10 mM sulfuric acid solution on thefilm. Subsequently, the cleavage fragments were removed from the NTdispersant free NT film by washing the film with deionized water. TheUV-visible spectrum of the resulting NT film displayed opticaltransparency of 70% at 550 nm, as shown in FIG. 7. Sheet resistancemeasurement for the 60 nm thick SWNT film shows similar properties tothat of a NT film prepared using the filtration method disclosed in U.S.Pat. No. 7,261,852, which is incorporated herein by reference. The SWNTfilm displays long term stability where the sheet resistance changedfrom 91.OMEGA./.quadrature. to only 167.OMEGA./.quadrature. after fourmonth of exposure to ambient air without any encapsulation, as shown inFIG. 8.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

1-27. (canceled)
 28. A patterned NT comprising film, comprising amultiplicity of NTs, wherein the NT's surfaces are free of residualdispersing agents allowing intimate electrical contact between the NTsthroughout the film and wherein the thickness of the film varies in apredetermined pattern.
 29. The NT comprising film of claim 28, whereinthe predetermined pattern comprises a series of lines or a gridcomprising less than 10% of the film's area connecting windowscomprising more than 90% of the film's area, wherein the lines or gridhave a transparency of less than 50% transmittance and the windows havea transparency in excess of 60% transmittance.